1. Field of the Invention
This invention relates generally to a photographic exposure control system having selectively actuatable ambient and flash modes and, more particularly, to a photographic exposure control system where the exposure control mode is determined as a function of whether the photographer chooses to light the scene by the available ambient scene light or artificial illumination.
2. Description of the Prior Art
Instant cameras embodying "scanning type" shutter blade arrangements have been used in conjunction with fixed focus objective lenses to provide a camera which is simple to operate. One camera of this type is currently marketed by Polaroid Corporation under the trade name "OneStep". This camera utilizes film units of the self-processable type which are automatically processed and ejected from the camera by way of a motorized drive mechanism. Thus, the photographer need only depress a single button to effect both the exposure and processing of the film units.
An exposure control for a camera of the aforementioned type having scanning shutter blade elements driven by a walking beam to provide a progressive variation in effective exposure and light sensing apertures is disclosed in U.S. Pat. No. 4,104,653, entitled "Scanning Shutter Blade Arrangement with Ambient and Flash Ranges", by Bruce K. Johnson et al., issued Aug. 1, 1978, in common assignment herewith and now incorporated by reference herein. Control is provided by the aforementioned exposure control system so that, when in an artificial scene-lighted mode of operation, the scanning shutter blades define an effective exposure aperture which progressively increases toward a maximum f/ stop at the largest aperture within a range of progressively increasing sized apertures. By contrast, when in a natural ambient scene-lighted mode of operation, the control provides for the scanning shutter blades to define an effective exposure aperture which progressively increases to a predetermined aperture size less than the maximum effective aperture size to which the shutter blade elements progress during the artificial scene-lighted mode. In this manner, there is maintained an increased depth of field during the ambient scene-lighted mode of operation where the camera-to-subject distances would be expected to be greater than during the artificial scene-lighted mode. Exposure control is provided by a photoresponsive element which receives incident scene light by way of a single, effective photocell sweep aperture defined by a pair of overlapping secondary apertures in respective blade elements.
U.S. Pat. No. 4,147,418, entitled "Photographic Exposure Control System with Independent Ambient and Artificial Illumination Control Modes", by George D. Whiteside, issued Apr. 3, 1979, in common assignment herewith and now incorporated by reference herein, shows an exposure control system embodying a scanning type shutter blade arrangement wherein the scene light is admitted to a photoresponsive element through a first pair of overlapping photocell sweep apertures during the ambient scene-lighted mode of operation and through a second pair of overlapping photocell sweep apertures during the artificial scene-lighted mode of operation. Thus, two entirely independent and different sets of photocell sweep secondary apertures control the admission of scene light to the photoresponsive element in correspondence with the scene light admitted by the primary aperture to the film plane solely as a function of whether the camera is operated in an ambient scene-lighted mode or an artificially scene-lighted mode. However, in this arrangement the maximum size to which the primary scene light admitting aperture is allowed to progressively increase is the same for either the ambient scene-lighted mode or the artificially scene-lighted mode, and hence there is provided no increased depth of field by limiting the size to which the scanning shutter blade elements may progressively open during the ambient scene-lighted mode of operation which would be particularly advantageous for a camera of the fixed focus type such as the aforementioned OneStep camera.
Therefore, it is a primary object of this invention to provide a photographic exposure control system embodying a scanning shutter blade arrangement in which the scene light is admitted to a photoresponsive element by way of a first pair of overlapping photocell sweep secondary apertures during an ambient scene-lighted mode of operation and in which the scene light is admitted to the photoresponsive element by way of a second pair of overlapping photocell sweep secondary apertures during the artificial scene-lighted mode of operation.
It is a further object of this invention to provide an exposure control system with a scanning shutter blade system wherein the range within which the primary aperture is allowed to progressively increase is limited during the ambient scene-lighted mode of operation in comparison to the range within which the primary aperture is allowed to progressively increase during the artificial scene-lighted mode of operation.
Other objects of the invention will be in part obvious and will in part appear hereinafter. The invention accordingly comprises a mechanism and system possessing a construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.